1. Field of the Invention
The present invention relates to a vertical nitride semiconductor light emitting diode (LED) and a method of manufacturing the same, which can improve electrical and optical characteristics at the same time.
2. Description of the Related Art
Generally, a nitride-based semiconductor LED is grown on a sapphire substrate, but the sapphire substrate is a rigid nonconductor and has poor thermal conductivity. Therefore, there is a limitation in reducing the manufacturing costs by decreasing the size of a nitride-based semiconductor LED, or improving the optical output of power and chip characteristic. Particularly, because the application of a high current is essential for achieving high power LED, it is important to solve a heat-sink problem of the LED. To solve this problem, there has been proposed a vertical nitride-based LED in which a sapphire substrate is removed by using a laser lift-off (LLO) process.
Hereinafter, a conventional nitride-based semiconductor LED will be described in detail with reference to FIG. 1.
FIG. 1 is a sectional view illustrating the structure of the conventional nitride-based semiconductor LED.
As shown in FIG. 1, the nitride-based semiconductor LED has a structure support layer 200 formed in the lowermost portion thereof.
On the structure support layer 200, a positive electrode (p-electrode) 150 is formed. Preferably, the p-electrode 150 is formed of metal with high reflectance so as to serve as an electrode and a reflecting layer.
On the p-electrode 150, a p-type nitride semiconductor layer 140, an active layer 130, and an n-type nitride semiconductor layer 120 are sequentially formed.
On the surface of the n-type nitride semiconductor layer 120, irregularities for enhancing light extraction efficiency are formed. On the n-type nitride semiconductor layer 120 having the irregularities thereon, a negative electrode (n-electrode) 160 is formed.
In a method of manufacturing the conventional nitride-based semiconductor LED, a buffer layer (not shown), the n-type nitride semiconductor layer 120, the active layer 130, and the p-type nitride semiconductor layer 140 are sequentially formed on a sapphire substrate (not shown).
Generally, the buffer layer may not be doped with impurities or may be doped in low concentration. Alternately, the buffer layer may be formed with a laminated structure composed of a layer which is not doped with impurities and a layer doped in low concentration. Further, the n-type nitride semiconductor layer 120 is doped with impurities in high concentration.
Then, the p-electrode 150 and the structure support layer 200 are sequentially formed on the p-type nitride semiconductor layer 140. Then, the sapphire substrate is removed through an LLO (laser lift-off) process so as to expose the buffer layer.
Then, the buffer layer and the n-type nitride semiconductor layer 120 are etched so that irregularities are formed on the surface of the n-type nitride semiconductor layer 120. At this time, the etching is performed so that the buffer layer does not remain on the n-type nitride semiconductor layer 120. That is because the highly-doped n-type nitride semiconductor layer 120 should be caused to come in contact with the subsequent n-electrode 160, thereby reducing contact resistance of the n-electrode 160 and an operation voltage.
However, in the process where the etching is performed so that the irregularities are formed on the surface of the n-type nitride semiconductor layer 120, when the depth of etching is not properly controlled, for example, when even the buffer layer 130 is etched, a short-circuit defect occurs, thereby reducing an electrical characteristic of an LED.
To solve this problem, a highly-doped n-type nitride semiconductor layer 120 is formed to have a large thickness such that an etching margin is secured. However, this method degrades a characteristic of the active layer 130. Further, although etching is performed without a short-circuit defect, it is difficult to form the n-electrode 160 on the surface having irregularities formed thereon. Further, an electric current is crowded into the irregular-surface structure in the lower portion of the n-electrode 160, thereby reducing a life span of an LED.
There is provided another method. In this method, a sapphire substrate is removed through an LLO process so as to expose a buffer layer, irregularities are formed on the buffer layer through a wet-etching process, a region of the buffer layer in which an n-electrode is formed is etched so as to expose the n-type nitride semiconductor layer, and the n-electrode is formed on the exposed n-type nitride semiconductor layer. In this case, since the forming of the irregularities is performed before the forming of the n-electrode, damage of the n-electrode caused by the forming of the irregularities can be prevented. However, the irregular profile on the surface of the buffer layer can be reflected on the surface of the n-type nitride semiconductor layer as it is. Therefore, it is difficult to form the n-electrode on a flat surface, and it is not easy to control the depth of etching.